The chlorococcal chlorophyte community structure and seasonal variations in terms of species composition and abundance of dominant species in Tatli, Gici, Liman, and Cernek lakes (Samsun, Turkey) were investigated between 1996 and 2003. Species richness and diversity (Shannon-Weaver, H') were measured monthly from stations at the surface of each lake. Changes in the Chlorococcales community structure were examined with nonmetric multidimensional scaling (NMDS) ordinations. A total of 36 Chlorococcales species were identified in these lakes located in the Kizilirmak Delta. While the Chlorococcales composition was similar in Tatli, Gici, and Liman lakes, Cernek Lake showed different seasonal trends, indicating high species richness. Ankistrodesmus falcatus and Kirchneriella obesa were important in terms of their contribution to the total Chlorococcales present in Tatli, Gici, and Liman lakes, and Monoraphidium irregulare had high concentrations among the Chlorococcales in Cernek Lake. There were clear increases in the species richness of Monoraphidium and Ankistrodesmus in all lakes during winter compared with other seasons.